1. Field of the Invention
The present invention relates to a light concentrating optical element that concentrates light having entered one surface thereof toward a side surface ranging along a side of the entry surface. It also relates to a light concentrating device, a photovoltaic power generation device and a photothermal conversion device, each equipped with the light concentrating optical element.
2. Description of Related Art
A solar cell that converts light energy to electric energy is constituted of a silicon-based material, a compound-based material, an organic material, a dye-sensitized material or the like. A standard solar cell normally achieves a power conversion efficiency of approximately 10 to 20%. The multi-junction solar cells developed in recent years, which include a plurality of semiconductor layers with optimal band gaps for photoelectric conversion of light in a plurality of wavelength bands defined by dividing the solar radiation spectrum range into a plurality of wavelength segments, laminated one layer on top of another, on the other hand, assure a much improved power conversion efficiency of up to 40%.
However, high-efficiency solar cells such as those described above are very expensive and thus, are not readily available except for special applications such as aerospace applications. As alternatives to the expensive, high-efficiency solar cells, concentration-type solar battery modules, enabling high-efficiency solar power generation at reduced cost by concentrating incident sunlight into compact cells, have been proposed. Japanese Laid Open Patent Publication No. 2005-142373 and Japanese Laid Open Patent Publication No. 2005-217224 disclose that, at a concentration-type solar cell module, sunlight focused via a Fresnel lens, a reflecting mirror or the like may be taken into the solar cells. U.S. Patent Application Publication No. 2006/0107993 discloses that fluorescent light generated in a fluorescent collector plate with fluorescing particles dispersed therein as sunlight is absorbed into the fluorescent collector plate may be guided toward a side of the plate and concentrated. U.S. Pat. No. 6,274,860 discloses that light diffracted through holographic film at a plate assembly with the holographic film and a solar cell enclosed therein as sunlight enters the plate assembly, may be guided to the solar cell through a spectral concentration system.